1. Field of the Invention
The present invention relates to a chip-type coil element, and more particularly, it relates to structure of a chip-type coil element which comprises a bobbin and a coil wound on the same.
2. Description of the Background Art
FIG. 4 is a sectional view showing a conventional chip-type coil element 1, which is of interest to the present invention. The coil element 1 comprises a bobbin 5 of a magnetic material such as ferrite, for example, having a core 2 and first and second flanges 3 and 4 which are provided on end portions of the core 2 respectively. The flanges 3 and 4 are in the form of quadrangular plates, for example. The first flange 3, which is shown in the lower part of FIG. 4, is larger in size than the second flange 4, which is shown in the upper part.
A coil 6 is wound on the core 2 of the bobbin 5. First and second electrodes 7 and 8 are provided on the lower flange 3, to be separated from each other. These electrodes 7 and 8 are adapted to extend from an end surface toward the side surface of the flange 3. First and second terminals 9 and 10 of the coil 6 are soldered to the first and second electrodes 7 and 8 respectively.
The coil element 1 is mounted on a circuit board 11, as shown in FIG. 6. Before operation for such mounting, solder paste members 14 and 15 are applied on circuit patterns 12 and 13, which are formed on the circuit board 11, in prescribed thickness by a method such as screen printing, as shown in FIG. 5. Then, the coil element 1 is placed on the solder paste members 14 and 15 while downwardly directing the lower surface of the lower flange 3. Thus, the coil element 1 is temporarily fixed to the circuit board 11 through the solder paste members 14 and 15. Then, the solder paste members 14 and 15 are reflowed to adhere to the lower and side surfaces of the flange 3 as shown in FIG. 6, thereby to completely mount the coil element 1 on the circuit board 11.
It has been recently required to reduce the volume of solder forming the solder paste members 14 and 15 in the operation for mounting the coil element 1. Thus, the solder paste members 14 and 15 may be reduced in thickness as shown in FIG. 7. When the solder paste members 14 and 15 are thus reduced in thickness, however, the volume of solder employable for connecting the electrodes 7 and 8 with the circuit patterns 12 and 13 is so decreased that the solder paste members 14 and 15 cannot cover the side surface of the flange 3. Thus, reliability in soldering is reduced.
When the volume of solder forming the solder paste members 14 and 15 is reduced, the coil element 1 tends to be inclined as shown in FIG. 9, in the so-called tombstoning phenomenon. Such a tombstoning phenomenon is caused by a lag in melting time between the solder paste members 14 and 15 in reflow soldering. When the left solder paste members 14 is molten in advance of the right solder paste member 15 as shown in FIG. 9, for example, torque is caused by surface tension of the molten solder member 14 to fulcrum the first terminal 9 for leftwardly inclining the coil element 1. Consequently, the coil element 1 is inclined as shown in FIG. 9, and hence the same cannot be mounted on the circuit board 11 in a desired mode. When the solder paste members 14 and 15 are increased in thickness as shown in FIGS. 5 and 6, such a tombstoning phenomenon is hardly caused since the coil element 1 is temporarily fixed through the solder paste members 14 and 15 with relatively strong force.